To meet challenges of wireless broadband technologies and maintain leading advantages of 3rd Generation Partnership Project (3GPP) networks, the 3GPP formulated a Long Term Evolution (LTE) plan for a mobile communications network at the end of 2004, and defined a new mobile communications network architecture under guidance of the evolution plan, as shown in FIG. 1. This architecture is more flattened than a second generation (2G) network and a third generation (3G) network, and retains only a packet switched (PS) domain. Therefore, this PS domain may be referred to as an evolved 3GPP packet switched domain (Evolved 3GPP Packet Switched Domain), or may be referred to as an evolved packet system (EPS).
A core network of the new mobile communications network, namely, an evolved packet core network (EPC), not only supports a 3GPP access technology, but also supports a non-3GPP (Non 3GPP) access technology, such as Code Division Multiple Access 2000 (CDMA2000), Worldwide Interoperability for Microwave Access (WiMAX), and a wireless local area network (WLAN).
In the existing network architecture (as shown in FIG. 1), when user equipment (UE) accesses the EPC from a non-3GPP side, the UE may perform access from a trusted non-3GPP side, or may perform access from an untrusted 3GPP side. Using access of UE from an untrusted 3GPP side (for example, access of UE from an untrusted WLAN) as an example, an evolved packet data gateway (ePDG) selects a packet data network gateway (P-GW) for an APN of the UE, and initiates a packet data network (PDN) connection setup procedure to the selected P-GW; through an S6b interface between the P-GW and a 3GPP authentication, authorization, and accounting server (3GPP Authentication, Authorization, and Accounting Server, 3GPP AAA Server), the P-GW sends an identity of the P-GW (namely, a P-GW ID) to the 3GPP AAA server; and then the 3GPP AAA server registers the received P-GW identity with a home subscriber server (home subscriber server/system, HSS). In this way, access from the untrusted 3GPP side is implemented.
However, in the prior art, the 3GPP AAA server needs to participate in the process of accessing the EPC network from the non-3GPP side by the UE. However, during subsequent network deployment, an operator hopes to simplify the network architecture as much as possible. For example, the 3GPP AAA server does not need to be deployed separately, and therefore, several 3GPP AAA related interfaces are not required. In this case, access of the UE from the non-3GPP side cannot be implemented based on the existing solution. This severely affects user experience.